Advancing PFAS characterization: Development and optimization of a UV-H2O2-TOP assay for improved PFCA chain length preservation and organic matter tolerance

As per- and polyfluoroalkyl substances (PFAS) infiltrate the environment via industrial, commercial, and domestic sources, the demand for robust, cost-effective, and straightforward analytical assays intensifies to enhance PFAS characterization and quantification. To address this demand, this study introduces a novel UV-H2O2-TOP assay, identifying optimal parameters such as pH (5-9), oxidant concentration (500 mM H2O2), activation rate (63 mM H2O2 h-1), and an acceptable total organic carbon (TOC) limit (~1000 mg/L TOC) to achieve maximum PFAA precursor conversion. Additional work was performed further optimizing the UV-TOP assay, by confirming its superiority to heat activation, identifying the effectiveness of different persulfate salts, and investigating different concentrations of sodium persulfate and sodium hydroxide at a 1:2.5 ratio on PFCA yield. Our investigation concluded by applying the UV-H2O2-TOP assay, using sodium persulfate as the TOP assay oxidant, to 6:2 FTS and five different AFFF samples. High-resolution mass spectrometry and an expanded analytical suite support sample analysis, facilitating direct quantification of ultra-short chain perfluoroalkyl carboxylates (PFCAs) and common fluorotelomer compounds including 5:3/5:1:2 fluorotelomer betaine and 6:2 fluorotelomer sulfonamido betaine. Results highlight several advantages of this tandem UV-activated method, including enhanced preservation of perfluoroalkyl chains (post-oxidation of 6:2 fluorotelomer sulfonate resulted in 28 % PFHpA, 47 % PFHxA, 25 % C3-C5 PFCA), capacity to handle high TOC limits (1000 mg/L TOC), and ability to incorporate higher persulfate concentrations in a single oxidation cycle.

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams

Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe₂O₄, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion.

Electron Paramagnetic Resonance for the Detection of Electrochemically Generated Hydroxyl Radicals: Issues Associated with Electrochemical Oxidation of the Spin Trap

For the detection of electrochemically produced hydroxyl radicals (HO^·) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO^· from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH^· adduct as formed from the solution reaction of OH^· with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap for OH^·. DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH^·) at potentials lower than that predicted thermodynamically (for water/HO^·) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH^· concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH^·, production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N-tert-butyl-α-phenylnitrone, α-(4-pyridyl N-oxide)-N-tert-butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application.

Ozonation/UV irradiation of dispersed Ag/AgI nanoparticles in water resources: stability and aggregation

Proliferation of nanoparticles (NPs) as aqueous pollutants is a matter of growing concern today. The aggregation kinetics of colloidal bare silver (Ag, 20.5 nm) and silver iodide (AgI, 15.3 nm) NPs were investigated during ozone/ultraviolet (O₃/UV) oxidation. Dynamic light scattering was applied to monitor the aggregation of NPs, and the z-average of treated samples was considered aggregate diameter. The effect of temperature, pH, and initial concentration of NPs was investigated on the aggregation rate constant and stability ratio. At a short oxidation period of approximately 1 min, the lower stability ratio was achieved for Ag NPs (< 50) than AgI NPs (> 100). Under acidic conditions, the negative surface charge of both NPs was neutralized that resulted in faster aggregation. In contrast, the impact of temperature and initial concentration of NPs on the aggregation rate was different for both NPs, which was due to the type of O₃/UV interaction with the surface of NPs and the thickness of the electrical double layer surrounding the NPs. The aggregation behavior of Ag NPs obeyed diffusion-limited regime, while an intermediate regime between diffusion- and reaction-limited was observed for AgI NP aggregation. The resulting aggregate morphologies showed that the clusters were ramified for Ag and compressed for AgI NPs. Applying the O₃/UV oxidation process for water treatment purposes leads to a significant reduction in aggregation time for inherently unstable Ag and stable AgI toxic NPs from several hours or days to several minutes.

Catalytic degradation of methylene blue by biosynthesized Au nanoparticles on titanium dioxide (Au@TiO2)

The degradation of methylene blue is a critical procedure in its wastewater remediation and thus has inspired wide catalysis research with semiconductors such as titanium dioxide (TiO₂) and rare metals such as gold (Au). In this study, we report bacterial cells assisting biosynthesis for Au@TiO₂ as an efficient catalyst for the catalytic degradation of methylene blue. Multiple complementary characterization for bio-Au_x@TiO₂ evidenced the evenly distributed Au nanoparticles (NPs) on the bio-TiO₂ layers. Meanwhile, bio-Au₂@TiO₂ displayed the superior catalytic activity in the degradation of methylene blue with the highest kinetics constant (k_app) value of 0.195 min^-1. In addition, bio-Au₂@TiO₂ keeps stable catalytic activity for up to 10 cycles. The origin of the catalytic activity was investigated by the hydroxyl radical fluorescence quantitative analysis and optical band gap analysis. In the bio-Au₂@TiO₂ catalytic system, Au NPs decreased the band gap energy of TiO₂ and enabled the generation of abundant photogeneration hydroxyl radicals, resulting in an enhanced photocatalytic activity. Our microbial synthesized bio-TiO₂ and bio-Au_x@TiO₂ study would be useful for developing green synthesis catalyst technology.

Green synthesis of magnetic activated carbon from peanut shells functionalized with TiO2 photocatalyst for Batik liquid waste treatment

The composite of magnetic activated carbon derived from peanut shells functionalized titanium dioxide (Fe3O4/TiO2/AC) has been successfully synthesized. The composite was employed to remove indigosol green and Cr(vi) under ultraviolet (UV) and visible light. In this work, the activated carbon was synthesized from a sustainable source of peanut shell by carbonization and activation method employing NaOH as the activating agent. Magnetite was prepared by chemical co-precipitation technique using FeCl3·6H2O and FeSO4·7H2O, and then, the deposition of TiO2 was performed under ultrasonic irradiation. A variety of material characterization, consisting of Fourier transform infrared, X-ray diffraction, and scanning electron microscopy-energy dispersive X-ray, was used to analyze the physicochemical properties of the composite. The effects of pH, irradiation time, and composite mass during optimization performance were investigated. The characterizations represent the dispersed TiO2 in the anatase phase with the existence of magnetic particles. The activity tests revealed the superiority of the composite for applications involving adsorption and photocatalysis under visible light source compared to UV light. It was found that Fe3O4/TiO2/AC yields the efficiency for the removal of indigosol green and Cr(vi) from Batik liquid waste of 92.91 and 76.92%, respectively.

Influence of pH on the Kinetics and Products of Photocatalytic Degradation of Sulfonamides in Aqueous Solutions

The aims of the study were to determine the kinetics of the photocatalytic degradation of six sulfonamides in the presence of TiO2-P25 in acidic, neutral, and alkaline solutions and to identify the structures of the stable products. It was stated that the pH of the solution significantly affected the photocatalytic degradation rate of sulfonamides in acidic and alkaline environments, and the effect likely depended on the susceptibility of sulfonamides to attack by hydroxyl radicals. In the post-reaction mixture, we identified the compounds resulting from the substitution of the aromatic rings with a hydroxyl group; the amide hydrolysis products; the hydroxylamine-, azo, and nitro derivatives; and the compounds formed via the elimination of the sulfone group. Moreover, previously unknown azo compounds were detected. Some degradation products of sulfonamides may exhibit marked bacteriostatic activity and high phytotoxicity. The azo and nitro compounds formed in an acidic environment may be potentially more toxic to aquatic ecosystems than the initial compounds.

Magnetoelectric dissociation of Alzheimer's β-amyloid aggregates

The abnormal self-assembly of β-amyloid (Aβ) peptides and their deposition in the brain is a major pathological feature of Alzheimer's disease (AD), the most prevalent chronic neurodegenerative disease affecting nearly 50 million people worldwide. Here, we report a newly discovered function of magnetoelectric nanomaterials for the dissociation of highly stable Aβ aggregates under low-frequency magnetic field. We synthesized magnetoelectric BiFeO₃-coated CoFe₂O₄ (BCFO) nanoparticles, which emit excited charge carriers in response to low-frequency magnetic field without generating heat. We demonstrated that the magnetoelectric coupling effect of BCFO nanoparticles successfully dissociates Aβ aggregates via water and dissolved oxygen molecules. Our cytotoxicity evaluation confirmed the alleviating effect of magnetoelectrically excited BCFO nanoparticles on Aβ-associated toxicity. We found high efficacy of BCFO nanoparticles for the clearance of microsized Aβ plaques in ex vivo brain tissues of an AD mouse model. This study shows the potential of magnetoelectric materials for future AD treatment using magnetic field.

Carbon dots dominated photoelectric surface in titanium dioxide nanotube/nitrogen-doped carbon dot/gold nanocomposites for improved photoelectrochemical water splitting

The dynamic behavior of electron-hole pairs at the interface of the nanocomposites is important for photoelectrochemical catalysis, but it is difficult to characterize. Here we construct a ternary titanium dioxide/nitrogen-doped carbon dot/gold (TiO₂/NCD/Au) complex as the model catalyst to investigate the kinetic indexes at their interfaces. Under irradiation (200 mW cm^-2), the photocurrent density of TiO₂/NCD/Au is 10.26 mA cm^-2, which is higher than those of TiO₂/Au (4.34 mA cm^-2), TiO₂/NCD (7.55 mA cm^-2) and TiO₂ (3.34 mA cm^-2). The evolved oxygen of TiO₂/NCD/Au reaches 125.8 μmol after 5000 s test. The energy bands of complexes are very similar to that of the unmodified TiO₂ catalyst due to the low content modification of NCDs and Au. In addition, the transient photovoltage (TPV) tests with a series of control samples show differences about the carriers' separation and transfer process, which verify that Au can increase the separation quantity of electron-hole pairs while NCDs play a more important role on the increase of the separation quantity and separation rate simultaneously. This work quantifies the function of each component in a composite catalyst and deepens the understanding of the catalyst interface design.

A Regioselectively Oxidized 2D Bi/BiOx Lateral Nano-Heterostructure for Hypoxic Photodynamic Therapy

Optoelectronic science and 2D nanomaterial technologies are currently at the forefront of multidisciplinary research and have numerous applications in electronics and photonics. The unique energy and optically induced interfacial electron transfer in these nanomaterials, enabled by their relative band alignment characteristics, can provide important therapeutic modalities for healthcare. Given that nano-heterostructures can facilitate photoinduced electron-hole separation and enhance generation of reactive oxygen species (ROS), 2D nano-heterostructure-based photosensitizers can provide a major advancement in photodynamic therapy (PDT), to overcome the current limitations in hypoxic tumor microenvironments. Herein, a bismuthene/bismuth oxide (Bi/BiOx)-based lateral nano-heterostructure synthesized using a regioselective oxidation process is introduced, which, upon irradiation at 660 nm, effectively generates ¹ O₂ under normoxia but produces cytotoxic •OH and H₂ under hypoxia, which synergistically enhances PDT. Furthermore, this Bi/BiOx nano-heterostructure is biocompatible and biodegradable, and, with the surface molecular engineering used here, it improves tumor tissue penetration and increases cellular uptake during in vitro and in vivo experiments, yielding excellent oxygen-independent tumor ablation with 660 nm irradiation, when compared with traditional PDT agents.

Combinatorial Analysis of Sparse Experiments on Photocatalytic Performance of Cement Composites: A Route toward Optimizing Multifunctional Materials for Water Purification

Blending TiO₂ and cement to create photocatalytic composites holds promise for low-cost, durable water treatment. However, the efficiency of such composites hinges on cross-effects of several parameters such as cement composition, type of photocatalyst, and microstructure, which are poorly understood and require extensive combinatorial tests to discern. Here, we report a new combinatorial data science approach to understand the influence of various photocatalytic cement composites based on limited datasets. Using P25 nanoparticles and submicron-sized anatase as representative TiO₂ photocatalysts and methyl orange and 1,4-dioxane as target organic pollutants, we demonstrate that the cement composition is a more influential factor on photocatalytic activity than the cement microstructure and TiO₂ type and particle size. Among the various cement constituents, belite and ferrite had strong inverse correlation with photocatalytic activity, while natural rutile had a positive correlation, which suggests optimization opportunities by manipulating the cement composition. These results were discerned by screening 7806 combinatorial functions that capture cross-effects of multiple compositional phases and obtaining correlation scores. We also report ^•OH radical generation, cement aging effects, TiO₂ leaching, and strategies to regenerate photocatalytic surfaces for reuse. This work provides several nonintuitive correlations and insights on the effect of cement composition and structure on performance, thus advancing our knowledge on development of scalable photocatalytic materials for drinking water treatment in rural and resource-limited areas.

Tailoring the Effects of Titanium Dioxide (TiO2) and Polyvinyl Alcohol (PVA) in the Separation and Antifouling Performance of Thin-Film Composite Polyvinylidene Fluoride (PVDF) Membrane

In this study, thin-film composite (TFC) polyvinylidene fluoride (PVDF) membranes were synthesized by coating with titanium dioxide (TiO₂)/polyvinyl alcohol (PVA) solution by a dip coating method and cross-linked with glutaraldehyde. Glutaraldehyde (GA) acted as a cross-linking agent to improve the thermal and chemical stability of the thin film coating. The incorporation of TiO₂ in the film enhanced the hydrophilicity of the membrane and the rejection of dyes during filtration. The layer of TiO₂ nanoparticles on the PVDF membranes have mitigated the fouling effects compared to the plain PVDF membrane. The photocatalytic performance was studied at different TiO₂ loading for the photodegradation of dyes (reactive blue (RB) and methyl orange (MO)). The results indicated that the thin film coating of TiO₂/PVA enhanced photocatalytic performance and showed good reusability under UV irradiation. This study showed that nearly 78% MO and 47% RB were removed using the TFC membrane. This work provides a new vision in the fabrication of TFC polymeric membranes as an efficient wastewater treatment tool.

Visible-Light Induced Sustainable Water Treatment Using Plasmo-Semiconductor Nanogap Bridge Array, PNA

The development of sustainable methods for energy-intensive water treatment processes continues to be a challenging issue. Plasmonic-semiconductor nanoparticles, which absorb large amounts of sunlight in the visible range for conversion into chemical energy efficiently, can form the basis of a sustainable water treatment method. However, the potential uses of plasmonic semiconductor particles for water treatment have not been fully explored yet because of the limitations associated with the imbalance between light capture, charge transfer, and the required recycling steps for the particles themselves. Herein, a significantly improved visible-light-induced water treatment method that uses a plasmo-semiconductor nanogap bridge array (PNA) is reported. As an arrangement of antenna-reactors, the PNA enables the balancing of the largely enhanced electromagnetic field in the plasmonic nanogap coupling region and optimal separation of charge carriers in the semiconductor. The simultaneous effects of visible-light absorption and charge transfer lead to the generation of a highly enhanced visible-light-induced OH radical (•OH). Consequently, visible-light-induced 5-log N/N₀ water disinfection and 100% chemical decomposition for sustainable water treatment were demonstrated. Owing to the large light absorption, charge carrier utilization, and array-oriented scalability, the PNA will be valuable in various sustainable energy and environmental applications.

Synthesis, structural characterization, docking simulation and in vitro antiproliferative activity of the new gold(III) complex with 2-pyridineethanol

Gold(III) complex containing 2-pyridineethanol has been synthesized and characterized structurally by single crystal X-ray diffraction, vibrational spectroscopy, ¹H NMR spectroscopy, electrochemical study, and DFT calculations. The Au(III) ion is four coordinated with one N-donor ligand (L) and three Cl anions. The Okuniewski's (τ'₄₌0.018) has been used to estimate the angular distortion from ideal square planar geometry. The vibrational spectroscopy studies, in the solid state and DMSO solution and cyclic voltammetry, have been performed to determine its stability and redox activity, respectively. A complete assignment of the IR and Raman spectra has been made based on the calculated potential energy distribution (PED). The theoretical calculations have been made for two functionals and several basis sets. The compound has been evaluated for its antiproliferative properties in a human lung adenocarcinoma cell line (A549), mouse colon carcinoma (CT26), human breast adenocarcinoma (MCF-7), human prostate carcinoma derived from the metastatic site in the brain (DU-145), and PANC-1 human pancreas/duct carcinoma cell line and non-tumorigenic cell lines: HaCat (human keratinocyte), and HEK293T (human embryonic kidney). Au(III) complex cytotoxicity is significantly against A549 and MCF-7 cells as in the reference drug: cisplatin. Studies of the interactions of Au(III) complex with DNA, HSA (human serum albumin) have been performed. The results from modeling docking simulations indicate that the title complex exerts anticancer effects in vitro based on different mechanisms of action to compare with cisplatin.

Hierarchical TiO2 Nanoflower Photocatalysts with Remarkable Activity for Aqueous Methylene Blue Photo-Oxidation

This study systematically evaluates the performance of a series of TiO₂ nanoflower (TNF) photocatalysts for aqueous methylene blue photo-oxidation under UV irradiation. TNF nanoflowers were synthesized from Ti(IV) butoxide by a hydrothermal method and then calcined at different temperatures (T = 400-800 °C) for specific periods of time (t = 1-5 h). By varying the calcination conditions, TNF-T-t photocatalysts with diverse physicochemical properties and anatase/rutile ratios were obtained. Many of the TNF-T-1 photocatalysts demonstrated remarkable activity for aqueous methylene blue photo-oxidation at pH 6 under UV excitation (365 nm), with activities following the order TNF-700-1 > TNF-600-1 > TNF-500-1 > TNF-400-1 ∼ P25 TiO₂ ≫ TNF-800-1. The activity of the TNF-700-1 photocatalyst (99% anatase, 1% rutile) was 2.3 times that of P25 TiO₂ at pH 6 and 14.4 times that of P25 TiO₂ at pH 4. Prolonged calcination of the TNFs at 700 °C proved detrimental to dye degradation performance due to excessive rutile formation, which reduced the photocatalyst surface area and suppressed OH^• generation. The outstanding activities of TNF-700-1 and TNF-600-1 are attributed to their hierarchical nanoflower morphology which benefitted UV absorption, a near-ideal anatase crystallite size for efficient charge separation, and their unusually low isoelectric point (IEP = 4.3-4.5).

ROS-mediated lipid peroxidation as a result of Cu(ii) interaction with FomA protein fragments of F. nucleatum: relevance to colorectal carcinogenesis

The ability of the studied FomA protein fragments of Fusobacterium nucleatum (Fn) with copper(ii) ions (Cu(ii)-Ac-KGHGNGEEGTPTVHNE-NH2 (1Cu) and its cyclic analogue Cu(ii)-cyclo(KGHGNGEEGTPTVHNE) (2Cu)) to induce reactive oxygen species (ROS) generation, as a result of red-ox processes, was determined by UV-Vis, luminescence methods, spin trapping and cyclic voltamperometry. The contribution of 1O2 and ˙OH to DNA degradation was proved using gel electrophoresis. Furthermore, the pronounced generation of ROS by mouse colon carcinoma cells (CT26) stimulated by both copper(ii) complexes was confirmed. A fluorescence method allowed the total amounts of ROS generated inside the CT26 cells to be detected, while the spin trapping technique proved that free radicals mainly attached to the membrane surface. These last results are in agreement with the data obtained from the ICP-MS method, which demonstrates that 1Cu and 2Cu complexes are not efficiently accumulated inside the cell. Furthermore, the role of ROS in lipid peroxidation was established. The above-mentioned factors may clearly indicate the contribution of ROS generated by the studied copper(ii) complexes to colonic cell damage, which can lead to a carcinogenesis process. This study may be an important step to recognize and understand the mechanism of colon cancer initiation.

Spectroscopic Measurements of Dissolved O3, H2O2 and OH Radicals in Double Cylindrical Dielectric Barrier Discharge Technology: Treatment of Methylene Blue Dye Simulated Wastewater

Advanced oxidation technologies (AOTs) focusing on nonthermal plasma induced by dielectric barrier discharge are adequate sources of diverse reactive oxygen species (ROS) beneficial for water and wastewater treatment. In this study, indigo, peroxytitanyl sulphate and terephthalic acid methods were used to approximate the concentrations of O3, H2O2 and OH produced in a double cylindrical dielectric barrier discharge (DCDBD) plasma configuration. The effect of pH and scavengers as well as the amount of chemical probes on the generation of oxidants was investigated. The efficiency of the DCDBD reactor was further evaluated using methylene blue (MB) as model pollutant. The results demonstrated that the formation of oxidants O3, H2O2 and OH in the DCDBD reactor was pH-dependent. Furthermore, the presence of scavengers such as phosphates, bicarbonates and carbonates in the solution diminished the amount of OH in the system and hence could impact upon the degree of detoxification of targeted pollutants during water and wastewater treatment. The MB simulated dye was totally decomposed into H2O, dissolved CO2 and simpler aqueous entities. Herein the DCDBD design is an adequate AOT that can be used worldwide for effective decontamination of water and wastewater.

A Comparative Study on Photocatalytic Degradation of Pyridinium – Based Ionic Liquid by TiO2 and ZnO in Aqueous Solution

The photocatalytic degradation of hexylpyridinium bromide (HPyBr) from an aqueous solution was studied by focusing on comparison of the photoactivity of ZnO and TiO2 P25. The process was carried out under different experimental conditions. The results showed that there is no adsorption of pollutant by both catalysts in the dark. The efficiency of P25 Degussa and ZnO photocatalysts were compared, and the photocatalytic kinetics study showed that ZnO is more efficient than TiO2 P25. The HPyBr photodegradation was found to follow a pseudo-first order kinetics, and the higher rates constants were obtained at the alkaline medium for ZnO (pH = 11, kapp = 9.61 × 10–2 min−1) and at acidic medium for TiO2 P25 (pH = 3, kapp = 1.28 × 10–2 min−1). The Langmuir–Hinshelwood model was found suitable to explain the rate constant data for the ionic liquid degradation by both catalysts. The presence of carbonate ions at alkaline medium was found to reduce the HPyBr degradation for ZnO and to enhance the HPyBr degradation for TiO2, this enhancement in TiO2/CO32-/UV system was confirmed by the addition of •OH and hvb+ scavengers. According to TOC and COD results, HPyBr mineralization was faster in ZnO/UV system than in TiO2/UV system.

Ascorbyl and hydroxyl radical generation mediated by a copper complex adsorbed on gold

Electrochemistry, nuclease assays, and EPR were used to detect ascorbyl and hydroxyl radical generation by a copper complex adsorbed on gold.

Improving the Photostability of Semiconducting Polymer Dots Using Buffers

The photostability of fluorescent probes is critical in biological imaging, especially for long-term observational analyses. Here, we describe a simple and universal method to improve the photostability of semiconducting polymer dots (Pdots) and other fluorescent probes by using buffers. Using Pdots as a model system, we found that HEPES or MES buffer can improve the photostability of Pdots by a factor of 20. Through a systematic study, we show that Pdot photobleaching is dominated by photoinduced radicals which can be quenched by the piperazine or morpholine structures of these buffers, which act as radical scavengers. For conditions where choice of buffer is limited, we designed fluorescent polymers conjugated with radical scavengers to improve Pdot photostability. We then demonstrate a practical application in which HEPES buffer is used to improve the photostability of Pdots during cell imaging.

Generation of hydroxyl radicals from reactions between a dimethoxyhydroquinone and iron oxide nanoparticles

The hydroxyl radical (·OH) is a powerful oxidant that is produced in a wide range of environments via the Fenton reaction (Fe²⁺  + H₂O₂ → Fe³⁺  + ·OH + OH^-). The reactants are formed from the reduction of Fe³⁺ and O₂, which may be promoted by organic reductants, such as hydroquinones. The aim of this study was to investigate the extent of ·OH formation in reactions between 2,6-dimethoxyhydroquinone (2,6-DMHQ) and iron oxide nanoparticles. We further compared the reactivities of ferrihydrite and goethite and investigated the effects of the O₂ concentration and pH on the generation of ·OH. The main finding was that the reactions between 2,6-DMHQ and iron oxide nanoparticles generated substantial amounts of ·OH under certain conditions via parallel reductive dissolution and catalytic oxidation reactions. The presence of O₂ was essential for the catalytic oxidation of 2,6-DMHQ and the generation of H₂O₂. Moreover, the higher reduction potential of ferrihydrite relative to that of goethite made the former species more susceptible to reductive dissolution, which favored the production of ·OH. The results highlighted the effects of surface charge and ligand competition on the 2,6-DMHQ oxidation processes and showed that the co-adsorption of anions can promote the generation of ·OH.

The Existence of Nitrate Radicals in Irradiated TiO2 Aqueous Suspensions in the Presence of Nitrate Ions

Evidence of the existence of nitrate radical in irradiated aqueous TiO₂ suspensions in the presence of nitrate ions are reported for the first time. The joint use of UV/Vis and EPR spectroscopy showed that nitrate radicals are formed by hole induced oxidation of nitrate ions. Photocatalytic degradation of a model alkene compound allowed to highlight the presence of an intermediate organic nitrate deriving from nitrate radical attack to the double bond of the substrate. These results not only allow deeper understanding of photocatalytic processes, but open the route to new green photocatalytic syntheses initiated by nitrate radicals and to new insights in the field of atmospheric chemistry.

Toward Eco-Friendly and Highly Efficient Solar Water Splitting Using In2S3/Anatase/Rutile TiO2 Dual-Staggered-Heterojunction Nanodendrite Array Photoanode

The TiO₂-based heterojunction nanodendrite (ND) array composed of anatase nanoparticles (ANPs) on the surface of the rutile ND (RND) array is selected as the model photoanode to demonstrate the strategies toward eco-friendly and efficient solar water splitting using neutral electrolyte and seawater. Compared with the performances in alkaline electrolyte, a non-negligible potential drop across the electrolyte as well as impeded charge injection and charge separation is monitored in the ANP/RND array photoanode with neutral electrolyte, which are, respectively, ascribed to the series resistance of neutral electrolyte, the fundamentally pH-dependent water oxidation mechanism on TiO₂ surface, as well as the less band bending at the interface of TiO₂ and neutral electrolyte. Accordingly, a TiO₂-based dual-staggered heterojunction ND array photoanode is further designed in this work to overcome the issue of less band bending with the neutral electrolyte. The improvement of charge separation efficiency is realized by the deposition of a transparent In₂S₃ layer on the ANP/RND array photoanode for constructing additional staggered heterojunction. Under illumination of AM 1.5G (100 mW cm^-2), the improved photocurrent densities acquired both in neutral electrolyte and seawater at 1.23 V vs reversible hydrogen electrode (RHE), which approach the theoretical value for rutile TiO₂, are demonstrated in the dual-staggered-heterojunction ND array photoanode. Faradaic efficiencies of ∼95 and ∼32% for solar water oxidation in neutral electrolyte and solar seawater oxidation for 2 h are acquired at 1.23 V vs RHE, respectively.

Modeling the pH and temperature dependence of aqueousphase hydroxyl radical reaction rate constants of organic micropollutants using QSPR approach

Designing of advanced oxidation process (AOP) requires knowledge of the aqueous phase hydroxyl radical (^●OH) reactions rate constants (k _OH), which are strictly dependent upon the pH and temperature of the medium. In this study, pH- and temperature-dependent quantitative structure-property relationship (QSPR) models based on the decision tree boost (DTB) approach were developed for the prediction of k _OH of diverse organic contaminants following the OECD guidelines. Experimental datasets (n = 958) pertaining to the k _OH values of aqueous phase reactions at different pH (n = 470; 1.4 × 10⁶ to 3.8 × 10¹⁰ M^-1 s^-1) and temperature (n = 171; 1.0 × 10⁷ to 2.6 × 10¹⁰ M^-1 s^-1) were considered and molecular descriptors of the compounds were derived. The Sanderson scale electronegativity, topological polar surface area, number of double bonds, and halogen atoms in the molecule, in addition to the pH and temperature, were found to be the relevant predictors. The models were validated and their external predictivity was evaluated in terms of most stringent criteria parameters derived on the test data. High values of the coefficient of determination (R ²) and small root mean squared error (RMSE) in respective training (> 0.972, ≤ 0.12) and test (≥ 0.936, ≤ 0.16) sets indicated high generalization and predictivity of the developed QSPR model. Other statistical parameters derived from the training and test data also supported the robustness of the models and their suitability for screening new chemicals within the defined chemical space. The developed QSPR models provide a valuable tool for predicting the ^●OH reaction rate constants of emerging new water contaminants for their susceptibility to AOPs.

Greywater as a sustainable water source: A photocatalytic treatment technology under artificial and solar illumination

Greywater considers being a highly reclaimable water source particularly important for water-stressed nations. In this work, heterogeneous photocatalysis using artificial and solar illumination has been applied for the mineralization of simulated light greywater (effluents from dishwashers and kitchen sinks were excluded from the study). The effects on the process' efficiency of TiO₂ P25 catalyst's concentration, initial concentration of H₂O₂ and Fe³⁺, pH of the solution, as well as the type of radiation, were evaluated in a bench-scale Pyrex reactor and a pilot-scale slurry fountain photoreactor. The treatment efficiency has been followed through the evolution of the organic matter content expresses as dissolved organic carbon (DOC). Best results were obtained with the photo-Fenton-assisted TiO₂ photocatalytic process with 72% DOC removal after 210 min of bench scale treatment, while under the same photocatalytic conditions in the pilot reactor the DOC removal reached almost 64%. Moreover, the decrease in toxicity, phytotoxicity and biodegradability of the simulated wastewater has been observed after solar-induced photocatalytic treatment.

Significant changes in the photo-reactivity of TiO2 in the presence of a capped natural dissolved organic matter layer

Natural dissolved organic matter (NDOM) in surface waters has a high sorption affinity for TiO₂ during long contact. An attached NDOM layer can act as a conduction band electron and/or valance band hole acceptor, and NDOM can also decrease the concentration of hydroxyl radicals (OH) in the bulk phase. Therefore, the degradation kinetics and mechanism for degradation of acetaminophen on NDOM capped TiO₂ (NDOM-TiO₂) are significantly different from those on raw TiO₂. Quantum calculation results suggest that hydroxylation to the ortho position in relation to the acetamide group is more favorable. Although OH induced hydroxylation is the predominant pathway for degradation of acetaminophen on TiO₂, one-electron oxidation of acetaminophen by a valance band hole, excited triplet NDOM or NDOM radical cation is the major degradation pathway on NDOM-TiO₂. This study is the first to detect and confirm APAP oligomers as intermediates during the degradation of acetaminophen by TiO₂ photocatalysis, especially when using NDOM-TiO₂ as a catalyst. The results suggest the reactivity of TiO₂ could change significantly after long exposure to natural water, which need to be concerned about for removal of micropollutants in surface water by TiO₂ photocatalysis.

Mechanistic Study of the Validity of Using Hydroxyl Radical Probes To Characterize Electrochemical Advanced Oxidation Processes

The detection of hydroxyl radicals (OH^•) is typically accomplished by using reactive probe molecules, but prior studies have not thoroughly investigated the suitability of these probes for use in electrochemical advanced oxidation processes (EAOPs), due to the neglect of alternative reaction mechanisms. In this study, we investigated the suitability of four OH^• probes (coumarin, p-chlorobenzoic acid, terephthalic acid, and p-benzoquinone) for use in EAOPs. Experimental results indicated that both coumarin and p-chlorobenzoic acid are oxidized via direct electron transfer reactions, while p-benzoquinone and terephthalic acid are not. Coumarin oxidation to form the OH^• adduct product 7-hydroxycoumarin was found at anodic potentials lower than that necessary for OH^• formation. Density functional theory (DFT) simulations found a thermodynamically favorable and non-OH^• mediated pathway for 7-hydroxycoumarin formation, which is activationless at anodic potentials > 2.10 V/SHE. DFT simulations also provided estimates of E° values for a series of OH^• probe compounds, which agreed with voltammetry results. Results from this study indicated that terephthalic acid is the most appropriate OH^• probe compound for the characterization of electrochemical and catalytic systems.

Vegetable Peel Waste for the Production of ZnO Nanoparticles and its Toxicological Efficiency, Antifungal, Hemolytic, and Antibacterial Activities

Zinc oxide (ZnO) nanoparticles (NPs) are important materials when making different products like sun screens, textiles, and paints. In the current study, the photocatalytic effect of prepared ZnO NPs from Moringa oleifera (M. oleifera) was evaluated on degradation of crystal violet (CV) dye, which is largely released from textile industries and is harmful to the environment. Preliminarily, ZnO NP formation was confirmed using a double beam ultraviolet visible (UV-Vis) spectrophotometer; further, the NP size was estimated using XRD analysis and the functional group analysis was determined using Fourier transform infrared (FT-IR) spectroscopy. The morphology of the synthesized NPs was found to be a hexagonal shape using SEM and TEM analysis and elemental screening was analyzed using EDX. ZnO NPs were shown sized 40-45 nm and spherical in shape. The degradation percentage of ZnO NPs was calculated as 94% at 70 min and the rate of the reaction -k = 0.0282. The synthesized ZnO NPs were determined for effectiveness on biological activities such as antifungal, hemolytic, and antibacterial activity. ZnO NPs showed good antifungal activity against Alternaria saloni and Sclerrotium rolfii strains. Further, we have determined the hemolytic and antibacterial activity of ZnO NPs and we got successive results in antibacterial and hemolytic activities.